This invention relates to a process for preparing tetrabromobis-phenol-A and to an improvement in a process for enhancing the purity of a flame retardant product predominant in a tetrabromobisphenol-A.
4,4'-isopropylidenebis(2,6-dibromophenol) is a well known commercial flame retardant and is usually referred to as tetrabromobisphenol-A (hereinafter "TBBPA"). Products comprised predominantly of TBBPA are useful as flame retardants in many macromolecular formulations. The literature is replete with processes for the manufacture of TBBPA, see, for example, U.S. Pat. No. 3,029,291; U.S. Pat. No. 3,182,088; U. S. Pat. No. 3,234,289; U.S. Pat. No. 3,363,007; 3,546,302; U.S. Pat. No. 3,868,423; U.S. Pat. No. 3,929,907; U.S. Pat. No. 4,013,728; U.S. Pat. No. 4,036,894; U.S. Pat. No. 4,112,242; U.S. Pat. No. 4,180,684; U.S. Pat. No. 4,431,847; U.S. Pat. No. 4,451,675; U.S. Pat. No. 4,701,568; U.S. Pat. No. 4,990,321; U.S. Pat. No. 5,008,469; U.S. Pat. No. 5,059,726; U.S. Pat. No. 5,068,463; Japanese Kokai 2 (1990) 196,747; EPO 380,363; British Patent 949,306. Processes which produce a TBBPA predominant product having a particularly low organic impurity content are described in U.S. Pat. No. 4,628,124; U.S. Pat. No. 4,783,556; U.S. Pat. No. 4,909,997; U.S. Pat. No. 5,017,728; U.S. Pat. No. 5,059,722, and U.S. Pat. No. 5,138,103 incorporated herein by reference as if fully set forth. Most if not all of the foregoing processes describe the recovery of TBBPA from the reaction mass by adding water to precipitate the product.
While the processes described in the foregoing patents yield products which are useful for most flame retardant applications, there exists a need for a TBBPA predominant product having both low organic impurity and low ionic impurity. These low impurity TBBPA predominant products have particular application as flame retardants in polymers and plastics for the electronics industry.
A particularly useful process for enhancing the quality of a product predominant in TBBPA is disclosed in Application Ser. No. 614,372, filed Nov. 15, 1990, now U.S. Pat. No. 5,107,035.
There is also a need, due to impending environmental restrictions on the production and use of methyl bromide, for a process which substantially reduces the amount of methyl bromide formed as a coproduct when using methanol as reaction solvent. Accordingly, one object of this invention is to provide a facile economic means for substantially reducing the amount of methyl bromide coproduct formed without the need for substantial capital investment.